How dangerous is nitrite? In an aquarium setting, nitrite kills. You don’t see nitrite. You can’t smell it. The water look crystal clear. Yet, nitrite make the healthy, red gills turn to brick-red tissue. That’s brown blood disease. Look at color chart in the infographic above. That’s the warning sign of nitrite toxicity. Even a slight trace of pink indicates a problem.
Clear water isn’t always safe water. That’s what most new aquarists think. Nitrite tells them they’re wrong.
## How to Test and Fix Nitrite in Your Aquarium
Precision matters during the test. This step gets overlooked by many hobbyists. It take ten drops of reagent for this test. That’s more than the ammonia test. Make sure you count every single one. Use only tank water to rinse out your tube to prevent contamination. Fill up to the five milliliter line, then invert it and shake vigorously. Wait exactly five minutes. If you check earlier or later, the color will not be fully formed yet. Then, you are ready for the result. Don’t go too far or solution will become unnaturally darker. Panic sets in because now there’s a problem. The testing process itself demands precision that casual hobbyists often overlook. That is the key. This is chemistry. There is a narrow window where it works. More time doesn’t mean more accurate.
After the allotted time, bring out test tube into natural light. The color match reveals the health of the living community in your tank. Colorless or barely pink indicates a healthy population of beneficial bacteria. These guys efficiently break down the waste in the tank. That’s what all aquarists strive for, it’s the safe zone.
The filter struggle if the color is light pink. Your bioload exceeds the capability of the bacteria colony to keep up. You may have added fish too fast. Or you cleaned your filter media under running tap water, which kills the bacteria colonies living inside. Aerobic bacteria die upon contact with tap water.
Medium pink color indicates moderate stress, such as low immunity. Your fish becomes more susceptible to secondary infections (e.g., columnaris). This shows severe oxygen deprivation. If the color turns bright pink or even magenta, there’s no doubt about it, your fish is gasping at the surface because they’re suffering from severe oxygen deprivasion, even though there’s plenty of dissolved oxygen in the water.
So why is nitrite deadly? What does it do to fish? Nitrite reacts with hemoglobin (a component of fish blood). Specifically, it changes hemoglobin to methemoglobin. Methemoglobin cannot carry oxygen. So even if there’s plenty of oxygen in the water, the fish will suffocate. Literally.
This is what happens when you see common emergency responses such as adding aquarium salt and/or increasing aeration. Salt doesn’t get rid of nitrite. Rather, the chloride ions that make up salt compete with nitrite for absorption on the gills. It prevents them from entering the bloodstream. It buys you some time. It does nothing else. Still, you must make massive water changes to dilute the toxin. Also, you should of add some bottled bacteria to allow your filter to regain its capacity.
The recovery from a nitrite spike is not instantaneous. This is a marathon and not a sprint. Even when the test shows zero, your fish are still vulnerable for weeks. The gills have been damaged; the tissue must heal. Those precious few days/weeks require clean water conditions. Immune systems is still depressed.
The chart above breaks down the critical action thresholds. If you wait to see if it gets better or worse, your fish will experience mass mortality. You need to intervene immediately once detected. The best defense is a good offense. Set up a solid biological filter. That should be done before introduction of any shrimp or discus, etc. Don’t feed too much. Keep your bacterial colonies alive by caring for them regularily. Don’t remove all your filter media at one time.
If you realize that nitrite is an intermediate in the nitrogen cycle and is only transient, then you deal with it rather than panic about it. Always aim for zero on the test card. That indicates a well-balanced environment where waste is consumed prior to reaching dangerous levels. Clear water can be deceptive; however, test results are objective facts.
